Compressor or vacuum pump provided with a transmission

ABSTRACT

A compressor provided with a compressor element with a driven shaft, a motor with a drive shaft to drive the compressor element, and a transmission between the drive shaft and the driven shaft. The transmission includes a housing and at least a driven gearwheel that is mounted on the driven shaft and a drive gearwheel that is mounted on a drive shaft. The housing includes two separated chambers, a first chamber that is connected to the driven shaft and a second chamber which is separate from the first chamber. The first chamber is connected via a channel with the second chamber, whereby around the drive gearwheel or driven gearwheel, the second chamber is formed. The form of the second chamber is such that when the gearwheel in question rotates, a gas flow is created around this gearwheel which causes a negative pressure in the channel by the venturi effect.

The present invention relates to a compressor or vacuum pump providedwith a transmission.

BACKGROUND OF THE INVENTION

It is known that a transmission between a drive shaft of a motor and thedriven shaft of, for example, a rotor of a compressor element, isprovided with a housing in which the gearwheels of the transmission arelocated.

In order to ensure a proper operation, oil is injected in the housing ofthe transmission to serve as lubricant.

As the driven shaft runs from the compressor element to thetransmission, seals are provided between the compressor element and thetransmission.

However, there will always be some leakage flow, which means some airwill end up in the housing of the transmission thus causing a pressurebuild-up in the transmission.

It is important to get rid of such positive pressure as said sealsshould not be exposed to too big a pressure difference because this canaffect their proper operation.

If the pressure difference is too great it is possible that air willleak from the transmission to the compressor element. This air will alsocontain the injected lubricant.

Such situation needs to be avoided at all times, as this lubricant willunintentionally end up in the compressor element and cause thecompressed air generated by the compressor element, to be polluted inthis case with the lubricant.

Certainly, in the case of oil-free applications whereby pure compressedair is required, such situation is not tolerable.

The positive pressure could be let off into the atmosphere. This meansthat air with the lubricant ends up in the atmosphere. Such situation ispreferably to be avoided for oil-free applications, as this lubricantwill end up on or near the machine, and in so doing may accidentallyalso end up in the machine.

This is why the housing of the transmission is connected with an oilseparator, to be able to purify the oil-air mixture in the transmissionvia the oil separator and to let it off into the atmosphere. Theseparated oil can be channelled back to an oil reservoir, tosubsequently be injected back into the transmission.

In the known transmissions, use is made of compressed gas to obtainextraction from the transmission to the oil separator via a venturichannel.

Part of the compressed gas generated by the compressor is used for thiswhich is branched off to said venturi channel. Consequently, the oil-airmixture will be extracted from the transmission, whereby the compressedgas and the oil-air mixture are blown through a filter.

Naturally this implies a loss of efficiency of the machine.

Moreover, the branch can be interrupted or detach, such that the venturichannel loses its effect, such that no extraction to the oil separatortakes place.

Alternatively, it is also possible to obtain extraction via an external(electrical) source with, for example, a ventilator.

However, this solution also implies an extra consumption of electricity,and also an additional risk if the external source fails, for example,in case of a power failure or break in the cable.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a solution for atleast one of said and other disadvantages.

To this end, the invention relates to a compressor provided with acompressor element with a driven shaft and a motor with a drive shaft todrive the compressor element, said compressor further being providedwith a transmission between said drive shaft and said driven shaft,which transmission comprises a housing and at least a driven gearwheelthat is mounted on the driven shaft and a drive gearwheel that ismounted on a drive shaft, whereby the housing comprises two separatedchambers, i.e. a first chamber that is connected to the driven shaft anda second chamber which is separate from the first chamber, whereby thefirst chamber is connected via a channel with the second chamber,whereby around the drive gearwheel or driven gearwheel the secondchamber is formed, whereby the form of the second chamber is such thatwhen the gearwheel in question rotates, a gas flow is created aroundthis gearwheel which causes a negative pressure in the channel by theventuri effect.

Said gas flow around the gearwheel is also called “gearwind” and is anair flow or vortex that is generated by the rotating teeth of thegearwheel.

“The first chamber is connected with the driven shaft”, means that thischamber is located on the side of the driven shaft, such that said leakflows end up in this chamber.

A first advantage is that, because a negative pressure is created in thechannel, an extraction of gas and any lubricant will take place as itwere from said first chamber through the channel to the second chamber.

This provides the advantage that because of this the pressure in thefirst chamber can be kept low, at a slight positive or negativepressure, within the limits of the pressure difference over the sealsbetween the compressor element and the transmission.

In the second chamber, where the gas and the lubricant of the firstchamber end up, there will be a pressure build-up.

Another major advantage is that this system does not require anyexternal power source, i.e. compressed air or electricity.

This also means there is no risk of failure or defect by a shut-down ofthis external power source.

Furthermore, it is an automatic self-regulating system: the faster thegearwheels rotate, the more leakage flow there will be from thecompressor element to the transmission, and the extraction of the firstchamber will be greater the faster the gearwheels rotate.

This means that the level of extraction of the first chamber willautomatically adapt itself to the situation.

Preferably the gearwheels and the housing form a tight fit, to minimisethe leak path between the first chamber and the second chamber as muchas possible and to thus create a sufficiently big pressure differencebetween both chambers.

Preferably, the distance in a radial direction between the wall of thesecond chamber and the gearwheel in question is also greater in therotation direction of the gearwheel in question.

This will help to guide the “gearwind” generated by the gearwheel tothus increase the negative pressure in said channel.

In a practical embodiment the second chamber in the housing describedabove extends from 0° to 225° of the circumference of the gearwheel inquestion departing from the position of engagement of the gearwheels.

The embodiment described above minimises the vortex losses, such thatthe power required for the pressure build-up in the second chamber iscompensated, and the venturi effect in the channel is maximised toguarantee the negative pressure in the first chamber.

The invention also relates to a vacuum pump provided with a vacuum pumpelement with a driven shaft and a motor with a drive shaft to drive thevacuum pump element, said vacuum pump further being provided with atransmission between said drive shaft and said driven shaft, wherebysaid transmission comprises a housing and at least a driven gearwheelthat is mounted on the driven shaft and a drive gearwheel that ismounted on a drive shaft, and in that the housing comprises twoseparated chambers, i.e. a first chamber that is connected to the drivenshaft and a second chamber which is separate from the first chamber,whereby the first chamber is connected via a channel with the secondchamber, whereby around the drive gearwheel or driven gearwheel thesecond chamber is formed, whereby the form of the second chamber is suchthat when the gearwheel in question rotates a gas flow is created aroundthis gearwheel which causes a negative pressure in the channel by theventuri effect.

BRIEF DESCRIPTION OF THE DRAWINGS

With the intention of better showing the characteristics of theinvention, a few preferred embodiments of a compressor or vacuum pumpaccording to the invention are described hereinafter by way of anexample, without any limiting nature, with reference to the accompanyingdrawings, wherein:

FIG. 1 schematically shows a compressor according to the invention;

FIG. 2 shows the transmission of FIG. 1 in detail;

FIG. 3 shows a view according to the arrow F3 in FIG. 2 .

DETAILED DESCRIPTION OF THE INVENTION

The compressor 1 shown in FIG. 1 essentially comprises a compressorelement 2, a motor 3 and a transmission 4 between the compressor element2 and the motor 3.

The compressor element 2 is in this case a screw compressor element 2,which comprises a compressor element housing 5 and two co-operatingscrew rotors 6 a, 6 b, more specifically a male screw rotor 6 a and afemale screw rotor 6 b, the lobes 7 of which turn into each otherco-operatively.

Both rotors 6 a, 6 b are mounted with bearings by means of their shaft 8in the compressor element housing 5.

The shaft 8 of one of the rotors 6 b is extended and forms the drivenshaft 9.

This driven shaft 9 reaches into the housing 10 of the transmission 4,and the driven gearwheel 11 is mounted at the end of it.

In order to close off the compressor element 2 from the transmission 4,two seals 12 a, 12 b are mounted on the driven shaft 9: an oil seal 12 aand an air seal 12 b.

The motor 3 has a drive shaft 13 that reaches into the housing 10 of thetransmission 4 and on which a drive gearwheel 14 is mounted that engageson said driven gearwheel 11.

The transmission 4 comprises the aforementioned housing 10 with saidgearwheels 11 and 14 therein.

Of course, it is not excluded that in the housing 10 additionalgearwheels are mounted between the driven gearwheel 11 and the drivegearwheel 14.

Nor does this exclude that the motor 3 is located in the housing 10 ofthe transmission 4.

A filter element 16 is connected to the housing 10 of the transmission4, to be able to filter oil out of the oil-air mixture that is in thehousing 10 of the transmission 4.

In this case, but not necessarily, the housing 10 of the transmission 4is connected to an oil reservoir 15 to collect the injected oil and thisoil reservoir 15 is provided with a filter element 16.

Furthermore, the compressor 1 in the shown example is also provided withan oil circuit 17, which can return the oil collected in the oilreservoir 15 with an oil pump 18, i.e. the oil that flows back out ofthe housing 10 and the oil separated by the filter element 16, back tothe transmission 4 and/or the motor 3. Additionally, the oil circuit 17is also provided with an oil filter 19 to be able to remove impuritiesfrom the oil.

According to the invention the housing 10 of the transmission 4comprises two chambers 20 and 22. A first chamber 20 which is connectedto the driven shaft 9 and a second chamber 22 which is separate from thefirst chamber 20. This is shown in FIG. 2 .

As one can tell from FIG. 2 , the driven shaft 9 extends into the firstchamber 20.

The second chamber 22 is provided around the drive gearwheel 14. Thefirst chamber 20 is connected to this second chamber 22 via the channel21.

The form of the second chamber 22 is shown clearly in FIG. 3 .

In this case, the second chamber 22 is integrated in the wall 23 of thehousing 10 of the transmission 4.

However, it is also possible that the transmission 4 is provided with ashield that is mounted next to, around or against the gearwheel 14 andthat is provided with a form similar to the second chamber 22. Suchshield can be mounted in the housing 10. This provides the advantagethat nothing needs to be changed to a possible existing housing 10.

The second chamber 22 is such that the “gearwind” that is created byrotation of the drive gearwheel 14 is led along the channel 21 such thata negative pressure is caused in the channel 21 because of the venturieffect.

As can be seen in FIG. 3 , the second chamber 22 gets bigger in therotation direction of the drive gearwheel 14, as was indicated witharrow P. Said channel 21 also connects to the end of the second chamber22 as seen in the rotation direction P of the drive gearwheel 14, i.e.to its biggest end.

Both characteristics will ensure that said effect will be as optimal aspossible.

The second chamber 22 extends from 0° to approximately 225° of thecircumference of the drive gearwheel 14 in the rotation direction ofarrow P, starting from the engagement of the gearwheels.

Preferably, the rest of the circumference of the drive gearwheel 14forms a tight fit.

This will ensure that the vortex losses are reduced to a minimum.

As can be seen in FIG. 1 , the second chamber 22 is connected to thefilter element 16 that is connected to the transmission 4. This filterelement 16, for example, can be a venting filter or a liquid separatorthat is provided with a filter.

Because the oil separation in the filter element 16 is always linkedwith a certain drop in pressure the result will be a positive pressurein the second chamber 22.

This means extra vortex losses in the second chamber 22.

According to the form of the second chamber 22, as shown in FIG. 3 , thereduction of the vortex losses by the tight fit of the drive gearwheel14 and the extra vortex losses in the second chamber 22 due to pressurebuild-up over the filter element 16 will cancel each other out whichmeans no extra power of the motor 3 is necessary.

The operation of the compressor 1 is very simple and as follows.

During the operation of the compressor 1 the motor 3 will power thedrive gearwheel 14, whereby the movement via the driven gearwheel 11 istransferred to the driven shaft 9 of the compressor element 2.

Oil will be injected in the transmission 4 and possibly also the motor 3for the cooling and/or lubrication of the gearwheels 11, 14, bearingsand other parts.

The operation of the compressor 1 will result in a certain pressurebuild-up in the transmission 4, as the air seal 12 b on the driven shaft9 will allow a certain leakage flow in the direction of the compressorelement 2 toward the transmission 4.

Consequently, in the housing 10 of the transmission 4 there will be anoil-air mixture at an increased pressure.

The rotation of the drive gearwheel 14 will create a so-called“gearwind” in the chamber 22 whereby an air flow or vortex is generatedby the rotating teeth of the drive gearwheel 14.

By channeling this air flow along the channel 21 the venturi effect willcause a negative pressure in the channel 21.

As a result of this negative pressure, the first chamber 20 will besucked out as it were and the oil-air mixture in this chamber will endup in the second chamber 22 via the channel 21.

This causes a pressure difference between the first chamber 20 and thesecond chamber 22, whereby the pressure in the first chamber 20 will belower than the pressure in the second chamber 22.

The lower pressure in the first chamber 20 prevents the seals 12 a, 12 bon the driven shaft 9 from being exposed to too big a pressuredifference, such that it is avoided that the oil-air mixture can end upin the compressor element 2.

The oil-air mixture ends up in the second chamber 22, where a pressurebuild-up will take place due to the drop in pressure over the filterelement 16 after which the purified, oil-free air can be channeled out.

The oil separated in the filter element 16 can then be injected backinto the transmission 4 and/or the motor 3 via the oil circuit 17.

Although in the shown example the second chamber 22 is provided aroundthe drive gearwheel 14, it is not excluded that this chamber 22 isprovided around the driven gearwheel 11 or another gearwheel, ifpresent.

However, preferably this chamber 22 extends along the gearwheel 11, 14or another gearwheel, if present, with the greatest diameter and/or thegreatest peripheral speed.

As is visible in FIG. 3 , the drive gearwheel 14 in this case is greaterthan the driven gearwheel 11 and the second chamber 22 is therefore alsoprovided around the drive gearwheel 14.

The bigger gearwheel 14 will, after all, be able to create a greater gasflow, such that the negative pressure in the channel 21 is greater and abetter extraction of the first chamber 20 is obtained.

According to the invention is it not necessary that it concerns acompressor 1 that is provided with a transmission 4 according to theinvention. The machine could also be a vacuum pump.

The present invention is by no means limited to the embodimentsdescribed as an example and shown in the drawings, but a compressor orvacuum pump according to the invention, can be realised in all kinds offorms and dimensions, without departing from the scope of the invention.

The invention claimed is:
 1. A compressor comprising with a compressorelement with a driven shaft and a motor with a drive shaft to drive thecompressor element, said compressor further being provided with atransmission between said drive shaft and said driven shaft, which thetransmission comprising a housing and at least a driven gearwheel thatis mounted on the driven shaft and a drive gearwheel that is mounted onthe drive shaft, wherein the housing comprises two separated chambers, afirst chamber that is connected to the driven shaft and a second chamberwhich is separate from the first chamber, whereby the first chamber isconnected via a channel with the second chamber, whereby around thedrive gearwheel or driven gearwheel the second chamber is formed,whereby the form of the second chamber is such that when the gearwheelin question rotates a gas flow is created around this gearwheel whichcauses a negative pressure in the channel by a venturi effect; wherein adistance in a radial direction between a wall of the second chamber andthe gearwheel in question gets bigger in a rotation direction of thegearwheel in question.
 2. The compressor according to claim 1, whereinthe second chamber is integrated in a wall of the housing.
 3. Thecompressor according to claim 1, wherein the second chamber extendsalong the gearwheel with a greatest diameter and/or a greatestperipheral speed.
 4. The compressor according to claim 1, wherein thesecond chamber extends from 0° to 225° of a circumference of thegearwheel in question starting from a position of engagement of thegearwheels.
 5. The compressor according to claim 1, wherein an openingof the second chamber is 25% to 75% of a circumference of the gearwheelin question.
 6. The compressor according to claim 5, wherein the openingof the second chamber is 45% to 55% of the circumference of thegearwheel in question.
 7. The compressor according to claim 6, whereinthe opening of the second chamber is 50% of the circumference of thegearwheel in question.
 8. The compressor according to claim 1, whereinsaid channel connects to an end of the second chamber, as seen in arotation direction of the gearwheel in question.
 9. The compressoraccording to claim 1, wherein said second chamber is in connection witha filter element or the like connected to the transmission.
 10. A vacuumpump comprising with a vacuum pump element with a driven shaft and amotor with a drive shaft to drive the vacuum pump element, said vacuumpump further being provided with a transmission between said drive shaftand said driven shaft, wherein said transmission comprises a housing andat least a driven gearwheel that is mounted on the driven shaft and adrive gearwheel that is mounted on the drive shaft, and wherein thehousing comprises two separated chambers, a first chamber that isconnected to the driven shaft and a second chamber which is separatefrom the first chamber, whereby the first chamber is connected via achannel with the second chamber, whereby around the drive gearwheel ordriven gearwheel the second chamber is formed, whereby the form of thesecond chamber is such that when the gearwheel in question rotates a gasflow is created around this gearwheel which causes a negative pressurein the channel by a venturi effect; wherein a distance in a radialdirection between a wall of the second chamber and the gearwheel inquestion gets bigger in a rotation direction of the gearwheel inquestion.